Welcome to the forum.
Personally I would use a demijohn, the 6 gallon bucket will have too much headspace for me
Ps all plastic used needs to be food grade and if putting hot liquid in it have the HDPE logo on it
You can but i I agree with TB above there is a lot of headspace so probably best not to use it.
If you haven't got a Demijohn get a 5 litre bottle of spring water use the water to make the wine and only screw the cap on loosely so the CO2 can escape when fermenting.